The present invention concerns a press section of a paper machine provided with a frame construction which comprises, in a running direction of the paper web, first a front frame and after that a rear frame, and in connection with the front frame and rear frame and any possible intermediate frame, press rolls are mounted which form a relatively compact press roll combination in which there are press nips formed by these press rolls, and with press fabric being passed through these nips. The frame construction comprises an at least partially open space situated between the front and rear frames which are not directly connected to one another and above the press roll combination, with at least most of the press rolls in the press roll combination being replaceable through this space, which also facilitates replacement of the upper press fabric situated in connection therewith. A press roll or press rolls of the press roll combination is/or mounted in connection with a rear side of the front frame, while a smooth-faced center roll of the press is mounted in conjunction with the rear frame, preferably on a projecting part thereof, or is mounted upon a separate intermediate frame, the center roll forming a second nip in the press together with the press roll noted above, in the running direction of the web.
In connection with the present application, a compact press roll combination means a roll combination having rolls constituting press nips with one another, but between said rolls there being one or several straight runs of the web, on which the web is supported by a press fabric. Thus, in connection with the present application, the scope of the concept "compact roll combination" includes press sections marketed by Valmet both under the trademark "Sym-Press II" and under the trademark "Sym-Press 0".
In prior art compact press sections of a paper machine, such as the Valmet so-called Sym-Press (TM) press section, above the press rolls both at the service side and at the operating side of the paper machine, there have been horizontal beams which connect the front frame and the rear frame of the press permanently together. In this connection, and also in the following description, the front frame means the frame part that is situated in the running direction of the web at the front side of the press roll combination. In a corresponding manner, the rear frame means the frame part situated at the rear side of the press roll combination.
In connection with prior art frame parts of the press sections, difficulties have occurred in relation to the placement of both the press fabrics and of the press rolls. These problems have increased with the increase in the width of the paper machines, especially due to the fact that the press rolls have become ever longer and heavier. These problems have been increased by the fact that press fabrics which are made of plastic materials and which are rigid in the transverse direction have begun to be used ever increasingly. These press fabrics cannot be jammed into a bundle, because they would thereby become wrinkled and become unusable.
Beloit Corporation has attempted to solve the problems described above by means of a so-called "Flip-Top" (trademark of Beloit Corporation) frame construction. In this prior art frame construction for a press section, a top frame is used which is provided with a pivot shaft parallel to a transverse direction of the paper machine and situated above the press rolls, whereby either the top part of the front frame or the top part of the rear frame can be open around the pivot shaft. Both of these two top parts of the frame cannot be opened at the same time. By opening the top part of the front frame, it is possible to facilitate the replacement of the pick-up fabric of the press section and the replacement of the fabric that usually acts as the press fabric in the first nip and in the second nip.
Thereat, the top part of the rear frame is locked as a frame part on whose support the opening-dumping of the top part of the front frame takes place. Correspondingly, when the top part of the front frame is in the closed-lock position, the top part of the rear frame can be dumped so that the press fabric of the third press nip can be replaced. The lower fabric of the first nip which runs principally in the basement space, is replaced by means of arrangements known in and of themselves. The above "Flip-Top" construction can be characterized as a type of "drawbridge", which is opened around an articulated joint situated at middle of the bridge, and only one half of the bridge being opened at a time.
From Valmet publish FI Patent Applications Nos. 70,951 and 73,025, frame constructions for press sections are known in which the front frame and the rear frame are connected to each other and/or to an intermediate frame of the central roll in the press by means of various openable and closable intermediate frames. Such openable and closable intermediate frames are usable in themselves, but they have left room for further development.
In the prior art frame parts of a press action noted above, the frame that supports the second press roll is supported on a bearing block of the central roll by means of locking members which are locked by means of eyebolts or the equivalent. Such a construction is quite expensive to accomplish and it slows down the replacement of press rolls and felts, in particular of the pick-up felt, because the locking must always be detached before replacement and re-locked after the replacement
When compact press roll arrangements are used, problems of space are also encountered, because several different press rolls with their auxiliary devices must be accommodated in a relatively limited space. This is why it has been necessary to place the frame parts that connect the front frame and the rear frame to one another or to an intermediate frame, with their opening and closing means, in highly congested spaces which results in problems both in the construction and in the operation.